US5722794A - Float for floating flexible pipes - Google Patents

Float for floating flexible pipes Download PDF

Info

Publication number
US5722794A
US5722794A US08/604,963 US60496396A US5722794A US 5722794 A US5722794 A US 5722794A US 60496396 A US60496396 A US 60496396A US 5722794 A US5722794 A US 5722794A
Authority
US
United States
Prior art keywords
floating body
body according
foam
floating
angle
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
US08/604,963
Inventor
Hans-Werner Friederich
Winfried Hellmig
Uwe Maass
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Phoenix AG
Original Assignee
Phoenix AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Phoenix AG filed Critical Phoenix AG
Assigned to PHOENIX AKTIENGESELLSCHAFT reassignment PHOENIX AKTIENGESELLSCHAFT ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: FRIEDERICH, HANS-WERNER, HELLMIG, WINFRIED, MAASS, UWE
Application granted granted Critical
Publication of US5722794A publication Critical patent/US5722794A/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L11/00—Hoses, i.e. flexible pipes
    • F16L11/04—Hoses, i.e. flexible pipes made of rubber or flexible plastics
    • F16L11/12—Hoses, i.e. flexible pipes made of rubber or flexible plastics with arrangements for particular purposes, e.g. specially profiled, with protecting layer, heated, electrically conducting
    • F16L11/133—Hoses, i.e. flexible pipes made of rubber or flexible plastics with arrangements for particular purposes, e.g. specially profiled, with protecting layer, heated, electrically conducting buoyant

Definitions

  • the invention relates to a float for floating hoses, comprising a multilayered foam body surrounding the floating hose, a textile cover, the latter being present on the foam body and having in particular several crossed layers, as well as an outer covering consisting of an elastomer, a thermoplastic elastomer (TPE), or a thermoplastic material.
  • a float for floating hoses comprising a multilayered foam body surrounding the floating hose, a textile cover, the latter being present on the foam body and having in particular several crossed layers, as well as an outer covering consisting of an elastomer, a thermoplastic elastomer (TPE), or a thermoplastic material.
  • TPE thermoplastic elastomer
  • Floating bodies for floating hoses are currently manufactured as integrated floating bodies in a way such that the foam layers are fused or glued together, forming one unit.
  • a textile cover and an outer covering made of the above-mentioned materials are arranged on said floating body. In this connection, the two coverings are solidly joined with the actual hose body.
  • the floating body according to the invention is provided with an additional textile, transverse reinforcement extending at an angle of 75° to 90°, particularly 85° to 90° relative to the axis.
  • FIG. 1 shows an axial sectional view of a floating body with a useful basic structure
  • FIG. 2 shows an axial sectional view of a floating body with the segments (A, B);
  • FIG. 3 shows an axial sectional view of the foam body with the sections (C, D);
  • FIG. 4 shows an axial sectional view of the corner zone of the face area and the cylindrical body with the segments (E, F), and a reinforcement arranged on the outside;
  • FIG. 5 shows a radial sectional view of the floating body with strips arranged in the radial direction
  • FIG. 6 shows an axial sectional view of the floating body with rings arranged in the radial direction.
  • FIG. 7 shows a side view of the textile cover of the embodiment shown in FIG. 2;
  • FIG. 8 shows a side view of the textile cover of an alternative embodiment of the invention.
  • FIG. 9 shows a schematic view of the different angles of the textile cover within section XI shown in FIG. 7.
  • FIG. 1 shows the following layer structure of the floating body (1):
  • the transverse reinforcement (6) which is arranged between the textile cover (4) and the outer covering (5), is designed single-layered, whereby the rings, at an angle of 90°, are disposed closely against each other.
  • the textile cover (4) and the transverse reinforcement (6) are preferably made of polyamide or polyester.
  • the foam body particularly consists of a polyethylene foam.
  • the following materials are useful:
  • Elastomer Ethylene-propylene-diene copolymer (EPDM)
  • TPE Mixture of polyethylene and polypropylene
  • Thermoplastic Polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC).
  • the segments (A, B) shown in FIG. 2 have to be viewed in connection with the useful embodiments of the foam body (3) and the textile cover (4).
  • the segments (A, B) shown in FIG. 2 have to be viewed in connection with the useful embodiments of the foam body (3) and the textile cover (4).
  • the foam body (3) is alternately structured of hard segments A) and soft segments (B), whereby the segments (A) are hard in the zone of the face area.
  • the textile cover (4) has alternately an angle of 54° (segment A) and 65° (segment B) relative to the axis, whereby the angle in the zone of the face area amounts to 54° as shown in FIGS. 7 and 9.
  • the angle of the textile cover (4) may also be constant, whereby the angle relative to the axis usefully comes to 60° as shown in FIG. 8.
  • FIG. 3 shows the foam core (3), which, in the radial direction, is alternately structured of hard foam layers (C) and soft foam layers (D), whereby the outer layers (C) are hard.
  • the foam layers (C, D) may be partly fused with each other, and partly separated from each other by a sliding foil. If need be, one or several textile layers may be incorporated between the foam layers (C, D) as strength carriers particularly based on polyamide or polyester.
  • the foam body (3) is formed in the corner zone (7) of the face area and the cylindrical body by a soft foam segment (F) and a hard foam segment (E), whereby an outer reinforcement (8) is additionally present, the latter particularly being based on polyamide or polyester.
  • the floating hose itself is provided with a flange (9).
  • FIG. 5 shows the outer covering (5) of the floating body (1), whereby the strips (10) are mounted on the outside in the axial direction with spacing from each other, such strips consisting of a material highly resistant to abrasion.
  • FIG. 6, too shows the outer covering (5), whereby the rings (11) are mounted on the outside in the radial direction especially within the marking zone, such rings consisting of a material highly resistant to abrasion.

Abstract

A float (1) for floating flexible pipes has a multilayered foam body (3) that surrounds the floating flexible pipe (2), a textile cover (4) arranged on the foam body (3) and having in particular several transverse layers, and an outer covering (5) made of an elastomer, a thermoplastic elastomer or a thermoplastic material. The float (1) is further provided with a transverse textile reinforcement (6) that forms with the axis an angle from 75° to 90°, in particular from 85° to 90°.

Description

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a float for floating hoses, comprising a multilayered foam body surrounding the floating hose, a textile cover, the latter being present on the foam body and having in particular several crossed layers, as well as an outer covering consisting of an elastomer, a thermoplastic elastomer (TPE), or a thermoplastic material.
2. The Prior Art
Floating bodies for floating hoses are currently manufactured as integrated floating bodies in a way such that the foam layers are fused or glued together, forming one unit. A textile cover and an outer covering made of the above-mentioned materials are arranged on said floating body. In this connection, the two coverings are solidly joined with the actual hose body.
In connection with floating hoses structured in said way, the following damage can be observed due to external influences:
(a) The two coverings are torn off in the end zones as a result of very high axial stress.
(b) A radial fracture of the float (floating body) frequently occurs as a result of axial and dynamic stress as well as buckling stress, with simultaneous breakage of the two coverings.
(c) Partial abrasion as well as slitting on sharp objects causes tearing of the two coverings.
SUMMARY OF THE INVENTION
For the purpose of eliminating the aforementioned weak points and particularly for the purpose of increasing the resistance to slitting and the resistance to abrasion, the floating body according to the invention is provided with an additional textile, transverse reinforcement extending at an angle of 75° to 90°, particularly 85° to 90° relative to the axis.
BRIEF DESCRIPTION OF THE DRAWINGS
Now, the invention is explained in the following on exemplified embodiments with reference to the schematic drawings, in which:
FIG. 1 shows an axial sectional view of a floating body with a useful basic structure;
FIG. 2 shows an axial sectional view of a floating body with the segments (A, B);
FIG. 3 shows an axial sectional view of the foam body with the sections (C, D);
FIG. 4 shows an axial sectional view of the corner zone of the face area and the cylindrical body with the segments (E, F), and a reinforcement arranged on the outside;
FIG. 5 shows a radial sectional view of the floating body with strips arranged in the radial direction; and
FIG. 6 shows an axial sectional view of the floating body with rings arranged in the radial direction.
FIG. 7 shows a side view of the textile cover of the embodiment shown in FIG. 2;
FIG. 8 shows a side view of the textile cover of an alternative embodiment of the invention; and
FIG. 9 shows a schematic view of the different angles of the textile cover within section XI shown in FIG. 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the following layer structure of the floating body (1):
2 Floating hose
3 Foam body
4 Textile cover
5 Outer covering
6 Transverse textile reinforcement.
The transverse reinforcement (6), which is arranged between the textile cover (4) and the outer covering (5), is designed single-layered, whereby the rings, at an angle of 90°, are disposed closely against each other. The textile cover (4) and the transverse reinforcement (6) are preferably made of polyamide or polyester.
The foam body particularly consists of a polyethylene foam. With respect to the outer covering, the following materials are useful:
Elastomer: Ethylene-propylene-diene copolymer (EPDM)
TPE: Mixture of polyethylene and polypropylene
Thermoplastic: Polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC).
The segments (A, B) shown in FIG. 2 have to be viewed in connection with the useful embodiments of the foam body (3) and the textile cover (4). In detail:
In the axial direction, the foam body (3) is alternately structured of hard segments A) and soft segments (B), whereby the segments (A) are hard in the zone of the face area.
In the segments (A, B), the textile cover (4) has alternately an angle of 54° (segment A) and 65° (segment B) relative to the axis, whereby the angle in the zone of the face area amounts to 54° as shown in FIGS. 7 and 9.
Owing to such segmenting, the susceptibility of the floating body to wear is reduced to a considerable degree.
Within the framework of an alternative, the angle of the textile cover (4) may also be constant, whereby the angle relative to the axis usefully comes to 60° as shown in FIG. 8.
FIG. 3 shows the foam core (3), which, in the radial direction, is alternately structured of hard foam layers (C) and soft foam layers (D), whereby the outer layers (C) are hard. In their radial structure, the foam layers (C, D) may be partly fused with each other, and partly separated from each other by a sliding foil. If need be, one or several textile layers may be incorporated between the foam layers (C, D) as strength carriers particularly based on polyamide or polyester.
According to FIG. 4, the foam body (3) is formed in the corner zone (7) of the face area and the cylindrical body by a soft foam segment (F) and a hard foam segment (E), whereby an outer reinforcement (8) is additionally present, the latter particularly being based on polyamide or polyester. The floating hose itself is provided with a flange (9).
FIG. 5 shows the outer covering (5) of the floating body (1), whereby the strips (10) are mounted on the outside in the axial direction with spacing from each other, such strips consisting of a material highly resistant to abrasion.
FIG. 6, too, shows the outer covering (5), whereby the rings (11) are mounted on the outside in the radial direction especially within the marking zone, such rings consisting of a material highly resistant to abrasion.

Claims (20)

We claim:
1. Floating body for floating hoses said body having a face zone and a cylindrical body, comprising
a multilayered foam body surrounding the floating hose;
a textile cover arranged on the foam body and being designed multilayered and crossed; as well as
an outer covering made from a material selected from the group consisting of an elastomer, a thermoplastic elastomer and a thermoplastic material, wherein
the floating body is provided with an additional transverse textile reinforcement extending at an angle of 75° to 90° relative to the axis.
2. Floating body according to claim 1, wherein the transverse reinforcement is comprised of a plurality of single-layered rings, whereby the rings are disposed closely to each other at an angle of 90°.
3. Floating body according to claim 1, wherein the transverse reinforcement is arranged between the textile cover and the outer covering.
4. Floating body according to claim 1, wherein the textile cover and the transverse reinforcement are made from a material selected from the group consisting of polyamide and polyester.
5. Floating body according to claim 1, wherein the foam body consists of polyethylene foam.
6. Floating body according to claim 1 wherein the foam layers are, in their radial structure, partly fused with each other and partly separated from each other by a sliding foil.
7. Floating body according to claim 1 characterized in that the foam body, in the radial direction, is alternately structured from hard foam layers and soft foam layers, said foam body having hard outer layers.
8. Floating body according to claim 7 characterized in at least one textile layer is incorporated as a strength carrier between the foam layers.
9. Floating body according to claim 1 wherein in the axial direction, the foam body is alternately structured from hard segments and soft segments, whereby the segments are hard in the face zone of the floating body.
10. Floating body according to claim 1 wherein in the corner zone of the face area and the cylindrical body of the floating body, the foam body is formed by a soft foam segment arranged on a hard foam segment, and wherein an outer reinforcement is additionally present, such reinforcement being made from polyamide and polyester.
11. Floating body according to claim 1 wherein the layers of the textile cover are arranged at an angle of 54° to 65° relative to the axis.
12. Floating body according to claim 11 wherein the angle is constant and particularly amounts to 60°.
13. Floating body according to claim 11 wherein the course of the angle is segmented, and alternates at an angle of 54° and of 65°, whereby in the face area, the angle comes to 54°.
14. Floating body according to claim 1 wherein the outer covering consists of a weather- and aging-resistant elastomer.
15. Floating body according to claim 1 wherein the outer covering consists of a thermoplastic elastomer based on a polyethylene/polypropylene mixture.
16. Floating body according to claim 1 wherein the outer covering consists of a thermoplastic material selected from the group consisting of polyethylene, polypropylene and polyvinyl chloride.
17. Floating body according to claim 1 wherein strips consisting of a highly abrasion-resistant material are mounted on the outer covering in the axial direction, said strips being spaced from each other.
18. Floating body according to claim 1 wherein highly abrasion-resistant rings are mounted on the outer covering in the radial direction.
19. Floating body according to claim 14, wherein the outer covering is an ethylene-propylene-diene copolymer.
20. Floating body according to claim 1, wherein the angle is between 85° and 90° relative to the axis.
US08/604,963 1994-07-02 1995-06-29 Float for floating flexible pipes Expired - Fee Related US5722794A (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE4423299.3 1994-07-02
DE4423299 1994-07-02
PCT/DE1995/000831 WO1996001385A1 (en) 1994-07-02 1995-06-29 Float for floating flexible pipes

Publications (1)

Publication Number Publication Date
US5722794A true US5722794A (en) 1998-03-03

Family

ID=6522140

Family Applications (1)

Application Number Title Priority Date Filing Date
US08/604,963 Expired - Fee Related US5722794A (en) 1994-07-02 1995-06-29 Float for floating flexible pipes

Country Status (8)

Country Link
US (1) US5722794A (en)
EP (1) EP0715701B1 (en)
JP (1) JP3342493B2 (en)
DE (2) DE19523147A1 (en)
DK (1) DK0715701T3 (en)
ES (1) ES2125023T3 (en)
HU (1) HUT75355A (en)
WO (1) WO1996001385A1 (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2379681A (en) * 2001-09-17 2003-03-19 Balmoral Group Marine buoyancy unit
US6547907B1 (en) * 1997-10-31 2003-04-15 Phoenix Aktiengesellschaft Method for producing a rotationally symmetric body
US20040266290A1 (en) * 2001-09-15 2004-12-30 Robert Gibson Buoyancy element and module
US20110038672A1 (en) * 2007-05-16 2011-02-17 Christopher Steven West System and methods to install subsea structures
ITTV20110053A1 (en) * 2011-04-20 2012-10-21 Kiasma S R L CONDUCT FOR INTEGRATING DRAGGING A LOCKING DEVICE
US20130137321A1 (en) * 2011-11-25 2013-05-30 Sercel Underwater floating device
RU2597733C2 (en) * 2014-10-15 2016-09-20 Михаил Иосифович Трибельский Floating pipeline
RU174137U1 (en) * 2016-04-13 2017-10-03 Общество с ограниченной ответственностью "Научно-производственное объединение "Композит" FLOATING PIPELINE

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE59801351D1 (en) 1997-11-14 2001-10-04 Phoenix Ag FLOATING BODY FOR SWIMMING HOSES

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE940787C (en) * 1954-09-03 1956-03-29 Bayer Ag Floating body made of polyurethane foam
FR1240554A (en) * 1959-07-25 1960-09-09 Lincrusta Submarine pipe laying process
US3594835A (en) * 1969-09-17 1971-07-27 Pipeline Products And Services Float device for pipelines
FR2091733A5 (en) * 1970-05-20 1972-01-14 Pirelli
FR2306394A1 (en) * 1975-04-02 1976-10-29 Hitters Christiaan Plastic floats for rigid or flexible floating pipeline plastic - with foam tubular core and glass fibre reinforced polyester envelope
US4107933A (en) * 1976-06-04 1978-08-22 Compagnie Generale Pour Les Developpements Operationnels Des Richesses Sous-Marines "C. G. Doris" Apparatus and method for towing a pipeline in a body of water
DE3333522A1 (en) * 1983-09-16 1985-04-04 Phoenix Ag, 2100 Hamburg HOSE WITH INCORPORATED CONNECTORS
EP0216418A1 (en) * 1985-09-04 1987-04-01 Wavin B.V. Foam plastics float for locally supporting a conveying line, and a floating conveying line
US4706711A (en) * 1984-09-12 1987-11-17 Taurus Gumiipari Vallalat Elastic technical hose with a foam insert

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE940787C (en) * 1954-09-03 1956-03-29 Bayer Ag Floating body made of polyurethane foam
FR1240554A (en) * 1959-07-25 1960-09-09 Lincrusta Submarine pipe laying process
US3594835A (en) * 1969-09-17 1971-07-27 Pipeline Products And Services Float device for pipelines
FR2091733A5 (en) * 1970-05-20 1972-01-14 Pirelli
FR2306394A1 (en) * 1975-04-02 1976-10-29 Hitters Christiaan Plastic floats for rigid or flexible floating pipeline plastic - with foam tubular core and glass fibre reinforced polyester envelope
US4107933A (en) * 1976-06-04 1978-08-22 Compagnie Generale Pour Les Developpements Operationnels Des Richesses Sous-Marines "C. G. Doris" Apparatus and method for towing a pipeline in a body of water
DE3333522A1 (en) * 1983-09-16 1985-04-04 Phoenix Ag, 2100 Hamburg HOSE WITH INCORPORATED CONNECTORS
US4706711A (en) * 1984-09-12 1987-11-17 Taurus Gumiipari Vallalat Elastic technical hose with a foam insert
EP0216418A1 (en) * 1985-09-04 1987-04-01 Wavin B.V. Foam plastics float for locally supporting a conveying line, and a floating conveying line

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6547907B1 (en) * 1997-10-31 2003-04-15 Phoenix Aktiengesellschaft Method for producing a rotationally symmetric body
US20040266290A1 (en) * 2001-09-15 2004-12-30 Robert Gibson Buoyancy element and module
US7214114B2 (en) 2001-09-15 2007-05-08 Trelleborg Crp Ltd. Buoyancy element and module
US20080017385A1 (en) * 2001-09-15 2008-01-24 Robert Gibson Buoyancy element and module
GB2379681A (en) * 2001-09-17 2003-03-19 Balmoral Group Marine buoyancy unit
US6821055B2 (en) 2001-09-17 2004-11-23 Crp Group Limited Marine buoyancy modules and units
US20110038672A1 (en) * 2007-05-16 2011-02-17 Christopher Steven West System and methods to install subsea structures
ITTV20110053A1 (en) * 2011-04-20 2012-10-21 Kiasma S R L CONDUCT FOR INTEGRATING DRAGGING A LOCKING DEVICE
US20130137321A1 (en) * 2011-11-25 2013-05-30 Sercel Underwater floating device
CN103129414A (en) * 2011-11-25 2013-06-05 瑟塞尔公司 Underwater floating device
US8893637B2 (en) * 2011-11-25 2014-11-25 Sercel Underwater floating device
US9394042B2 (en) 2011-11-25 2016-07-19 Sercel Underwater floating device
RU2592956C2 (en) * 2011-11-25 2016-07-27 Серсел Underwater floating device
CN103129414B (en) * 2011-11-25 2016-12-21 瑟塞尔公司 Flotation gear under water
RU2597733C2 (en) * 2014-10-15 2016-09-20 Михаил Иосифович Трибельский Floating pipeline
RU174137U1 (en) * 2016-04-13 2017-10-03 Общество с ограниченной ответственностью "Научно-производственное объединение "Композит" FLOATING PIPELINE

Also Published As

Publication number Publication date
WO1996001385A1 (en) 1996-01-18
DE59503850D1 (en) 1998-11-12
HUT75355A (en) 1997-05-28
EP0715701A1 (en) 1996-06-12
ES2125023T3 (en) 1999-02-16
DK0715701T3 (en) 1999-06-21
JPH09502507A (en) 1997-03-11
EP0715701B1 (en) 1998-10-07
JP3342493B2 (en) 2002-11-11
HU9600489D0 (en) 1996-04-29
DE19523147A1 (en) 1996-01-04

Similar Documents

Publication Publication Date Title
US5052444A (en) Reinforced fluid hose having on-bonded tape
US5148836A (en) Flexible hose construction
US7322379B2 (en) Flexible kink-resistant hoses
US6390140B2 (en) Fluid-impermeable composite hose
US3856052A (en) Hose structure
US5722794A (en) Float for floating flexible pipes
US5894865A (en) Flexible hose construction and method of making the same
US4487232A (en) Doubled-walled corrugated synthetic resin pipe
US3604461A (en) Composite tubing
US3902531A (en) Buoyant hose
US4644977A (en) Hose with coextruded cover consisting of multiple foamed or nonfoamed layers
WO1992016355A3 (en) Flexible tubular structure
GB2175308A (en) Hose
EP0032352B1 (en) Hose structure
US3871408A (en) Oil suction and discharge hose
JP2006194430A (en) Pressure hose
US4461324A (en) Rubber hose
US3811477A (en) Buoyant liquid-conveying hose
US5275208A (en) Flexible hose construction and method of making the same
JPH06147368A (en) Hose
USRE32508E (en) Hose structure
US4240653A (en) Flexible expansion joint
US3868974A (en) Reinforced flexible articles
EP0670980B1 (en) Hose end fitting and hose assembly
SE461293B (en) ROUTES FOR LINING OF MARKETING PIPES

Legal Events

Date Code Title Description
AS Assignment

Owner name: PHOENIX AKTIENGESELLSCHAFT, GERMANY

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FRIEDERICH, HANS-WERNER;HELLMIG, WINFRIED;MAASS, UWE;REEL/FRAME:007912/0341

Effective date: 19960216

FPAY Fee payment

Year of fee payment: 4

REMI Maintenance fee reminder mailed
LAPS Lapse for failure to pay maintenance fees
STCH Information on status: patent discontinuation

Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362

FP Lapsed due to failure to pay maintenance fee

Effective date: 20060303